M8.9 Earthquake Near the East Coast of Honshu, Japan

A massive, magnitude 8.9 earthquake struck the Japan Trench megathrust fault off the eastern coast of Honshu Friday, March 11 at 2:46 pm local time. The quake struck about 80 miles (125 kilometers) off Japan's eastern coast, approximately 240 miles (380 kilometers) northeast of Tokyo. Damage from this event is focused on the prefectures of Chiba (northern), Ibaraki, Tochigi, Fukushima, Miyagi, and Iwate (southern). The city of Sendai (1 million people) experienced the worst damage. Over 12 million people (10% of the total population of Japan) have been significantly affected by this event.

This is the second CatWatch notification/update issued by EQECAT for this event.

Recap of 11 March, 2011 Miyagi Earthquake

Economic losses continue to rise as significant earthquake-related events develop, including damage from numerous fires, and an explosion at a nearby nuclear plant. Total economic losses will likely exceed $100B USD. Key components of this will be extensive property damage to residential and commercial occupancies and restoration of critical infrastructure.

Ground Motions

This earthquake has affected a broad swath of Japan. The USGS has produced a peak ground acceleration ground motion map displaying their modeled estimate of the distribution of ground motions, as shown in the following figure. This map displays the geographic spread of damaging ground motions from Tokyo northward, and the extent to which ground motions extend across the island of Honshu. The scatter of points represent the epicenters and magnitudes of fore- and aftershocks in the area since March 5, 2011.

The USGS Pager system integrates this map with city populations to derive an estimate of the populations affected by ground motion intensities. This produces an estimate of 4 million people residing in areas affected by very strong ground motions. An additional 8 million people reside in areas affected by strong ground motions.

While the USGS provides modeled estimates of ground motion, the Japanese Meteorological Agency (JMA) provides instrumental (measured) ground motion for discrete locations. The JMA provides these ground motions using a different scale, but because this relies upon measured ground motions, it can provide a different perspective.

In the Sendai area JMA intensities of 6- and greater extend inland about 30 miles (50 km), as shown in the figure below:

The larger slip area on the mega-thrust fault affected a much larger on-land area than would be expected from any earthquake in the "Miyagi Offshore" source itself. For these reasons, no single event in EQECAT's event set for Japan will effectively replicate the area shaken by the Sendai earthquake. Since this massive earthquake apparently ruptured multiple segments of the megathrust system, EQECAT is working to develop a suitable ground motion footprint for this event. EQECAT's seismic model for the Miyagi Offshore included many different rupture zones and cascading zones. The events that model cascading ruptures of the A1, A2 and B segments are the closest representations of this fault zone, but they represent too low a magnitude (as noted above).

Based upon measured ground motion intensities, the prefectures most affected by this event (JMA 6) are Chiba (northern), Ibaraki, Tochigi, Fukushima, Miyagi and Iwate (southern). Prefectures with significant observations of JMA 5 include Tokyo, Kanagawa, Saitama, Niigata, Yamagata and Aita. This distinction is important - the most severe damage to property and assets is expected in the areas with JMA 6, but the areas of JMA5 are expected to have scattered pockets of damage throughout the region.

Tsunami

The earthquake triggered a 23-foot (7 meter) tsunami in nearby Sendai. Flooding from the waves extended more than six miles inland in some places, over-running the Sendai airport and causing massive, widespread damage to the city center. Several trains are missing, presumably swept away by the tsunami waves that crested the railroad tracks. Ports and cities along the north-eastern seaboard of Japan were impacted with devastating waves and flooding. The confirmed fatality count from this event is quickly approaching 1,000.

The tsunami damaged many port facilities, ranging from demolished piers and wharves to onshore storage facilities to transportation access via rail and highways. Marine losses will be extensive, with many large ships aground on Japan's eastern shore, and hundreds of smaller commercial and personal vessels. Automobile losses are extensive as the coastal populace had little time to evacuate.

Nuclear Power

Three power plants were within the area of high ground motions - Onagawa, north of Sendai, and two plants near Fukushima, the Fukushima Daiichi and Fukushima Daina plants. Radiation spills and explosions have been reported at the Fukushima Daiichi plant, and 500,000 residents within a 6 mile radius were evacuated Saturday.

Japan relies upon nuclear power for more than one-third of energy production, coming from 55 nuclear power plants distributed throughout the country. The vibrations from the earthquakes tripped 11 power plants off-line after the earthquake - shutdown is implemented to protect the rotating equipment and is a typical procedure. The plants require significant amounts of power to run cooling systems even when not generating electricity and the lack of power has contributed to the problems at the Fukushima Daiichi plant.

A shortage of electricity in this region will impair the restoration and increase the overall economic costs of this event. A release of radiation would likely affect mortality in the region for years.

Fires

Fires following earthquake are a persistent risk in Japan. Immediately following the earthquake there were at least 80 reports of major fires. A fire at a refinery in Ichihara city (Chiba) remains contained but active as of late Saturday (12 March). As of mid-day Saturday, 1.4 Million barrels per day of oil refinery capacity was still off-line, representing about 30% of Japan's total capacity.

There have been numerable fires in urban areas. The density of housing, a preference for wood structures, and the practice of cooking with kerosene lead to a heightened risk for fires ensuing from earthquake shaking. A fire fighting force that is over-whelmed by the demands for evacuation and immediate first aid contribute to a heightened risk for a single-house fire turning into a conflagration of many homes. The 1995 Great Hanshin (Kobe) earthquake saw residential housing fires consume thousands of homes.

Ground Shaking Damage

Access to many parts of the affected area is limited, but reports of damage to structures and facilities are coming in. Destroyed housing from the tsunami and shaking have led to tens of thousands of homeless people. Manufacturing plants in the region remain off-line, with reports of damage to several facilities. Significant damage has been observed to regional infrastructure ranging from roads, and major highways, and railroads. Railroads are primarily used for the transportation of people and most commercial traffic is by highway.

Economic Loss Estimation

Economic damages from this event will be devastating. Strong shaking has impacted over 12 million people, over 10% of the population. More than 2 million people live in cities that were over-run with flooding from the tsunami. Several ports were damaged, but these were not the largest ports in the country. The electrical power grid has sustained damage that will persist for weeks if not months and years. Petroleum refining capacity has sustained a short-term hit but most capacity could be restored within a month.

The eastern prefectures of Ibaraki, Tochigi, Fukushima, Miyagi and Iwate will suffer the most damage. Four million people residing in areas of very strong ground motion translates to approximately 2 million dwelling units. Most dwellings will be relatively undamaged, but 30% of these dwellings are expected to have damage ranging from minimal to severe. Property damage to dwellings alone is expected to exceed $20 Billion USD. Additional damage to contents, and living expenses for those who are forced to evacuate their houses, could double this figure.

Damage to commercial facilities is widespread. Several manufactures, including Honda, Toyota, Nissan and Sony have indicated that they have damaged and closed facilities. Restoration of production will require the re-settlement of displaced workers, repair of damage, and restoration of critical infrastructure such as power, highways and ports. We expect damage to commercial facilities to be approximately equal to residential damage.

Fire following economic losses will likely approach $5 to $10 Billion USD. Several large fires have produced significant impacts.

Tsunami losses will also include losses to automobiles. Approximately 1 million automobiles were registered in areas that suffered significant flood damages. If one-third of these are damaged from the tsunami, the property losses to automobiles could exceed several billion dollars. Including the flood losses to property, flooding losses will likely exceed $20 Billion USD.

Critical infrastructure damage has not been completely tallied. The experience from recent earthquakes demonstrates that much of this damage can be restored quickly if it is rapidly identified and repaired. The cumulative damage to infrastructure will likely exceed the damage to dwellings and run to $30 Billion USD or more.

Marine losses, including losses to port facilities could cost as much as $10 Billion USD. There are several large ports in the area, and thousands of boats have been run aground.

It is premature to produce insured loss estimates at this time. EQECAT is evaluating the event and its impacts and expects to release an estimate early the week of March 13.

Modeling This Earthquake

An earthquake of this magnitude is unprecedented in this region. While this megathrust fault has ruptured in 9 significant earthquakes since 1973, the largest of these have had magnitudes of 7.7 - 7.8 according to the USGS. The Japanese Headquarters for Earthquake Research Promotion (HERP) had estimated potential megathrust earthquakes in this region up to moment magnitude 8.25. Recent estimates by HERP put the probability of a magnitude 8.2 earthquake on the megathrust fault at 20% over the next 30 years. Thirty-year probabilities for a smaller earthquake of magnitude 7.7-7.9 in the "Miyagi offshore" seismic source that is located closer to the coast of Honshu was listed as high as 80% to 99%. That probability was fulfilled with the March 9, M 7.8 Miyagi earthquake, which in retrospect turned out to be a foreshock of the much larger M8.9 earthquake of March 11.

Friday's earthquake ruptured the megathrust fault plane between the descending Pacific and overriding continental tectonic plate, as shown in the figure below. The block diagram shows the complex plate tectonic setting of Japan. The red patch on diagram shows the general location of the M8.9 megathrust rupture.

Japan Earthquake Rupture Area - March 12, 2011

At the Japan Trench, the Pacific plate is converging with the continental plate at a rate of approximately 83 mm/yr. This convergence is not accommodated smoothly along the megathrust fault. Rather, the fault moves in what is referred to as "stick-slip" motion. Strain is built up along the fault plane over decades or centuries until the resistance to sliding is overcome. The plates then lurch past one another along the fault producing large megathrust earthquakes. Because of the unprecedented size of the March 11 earthquake, the rupture along the megathrust fault zone likely involved multiple segments previously defined by HERP and implemented in the EQECAT JapanQuake Model, shown below. This figure shows the names and locations of subduction seismic sources in Japan as defined by HERP and implemented in the EQECAT JapanQuake model. Because of the unprecedented size of the March 11 earthquake offshore of northern Honshu, the earthquake apparently ruptured multiple segments of the "Japan Trench Subduction Zone (S.Z.)" megathrust fault.

Japan Quake Fault Zones - March 12, 2011

The larger slip area on the mega-thrust fault affected a much larger on-land area than would be expected from any earthquake in the "Miyagi Offshore" source itself. For these reasons, no single event in EQECAT's event set for Japan will effectively replicate the area shaken by the Sendai earthquake. Since this massive earthquake apparently ruptured multiple segments of the megathrust system, EQECAT is working to develop a suitable ground motion footprint for this event. EQECAT's seismic model for the Miyagi Offshore included many different rupture zones and cascading zones. The events that model cascading ruptures of the A1, A2 and B segments are the closest representations of this fault zone, but they represent too low a magnitude (as noted above).

These event IDs are:

ID

System

Segment / Rupture

Mw

Epicenter Latitude

Epicenter Longitude

6046

Japan Trench

Miyagi (A1+ A2 + B)

M8.24

38.33

142.4

6045

Japan Trench

Miyagi (A1+ A2 + B)

M8.18

38.33

142.4

6044

Japan Trench

Miyagi (A1+ A2 + B)

M8.12

38.33

142.4

6043

Japan Trench

Miyagi (A1+ A2 + B)

M8.06

38.33

142.4

6042

Japan Trench

Miyagi (A1+ A2 + B)

M8.00

38.33

142.4

The reference event is a M8.9 (the USGS has not clarified if this is a moment magnitude) with epicenter at 38.32, 142.37, depth of 24 km. The epicenter is in the northern portion of the rupture plane.

The Sanriku to Boso segment of the Japan Trench is immediately south of the Miyagi ruptures. The HERP catalog included ruptures of up to magnitude 8.4 on this zone. Because these ruptures are further south and closer to Tokyo than the original rupture, EQECAT believes that these represent an upper bound on loss potential.